Extended algorithm documentation in constituent packages

[ChrisRackauckas]

There is much algorithm-specific information:

• What parts of the common interface are supported by each solver
• Extended information on the extra options each has available
• The documentation for their specific callbacks
• The types that the algorithm supports

I think we should follow JuliaOpt's lead and have this be documentation which is part of the solver packages themselves. So DifferentialEquations.jl would have a general overview of the packages which are available and help guide users to choices (like it is now), but each section would contain a link to the package's own documentation detailed information about all of the extra stuff (like the JuMP) documentation. This will allow all of the details to be documented without bloating the main docs.

[ChrisRackauckas]

Most of this was done by making stuff act more uniformly, and they all have READMEs now.